What is an Ovulation Calculator?
An Ovulation Calculator estimates your likely ovulation day and fertile window from the first day of your last period and your average cycle length.
Ovulation usually happens about 14 days before the next period. The fertile window covers the five days before ovulation and the day after. Cycles vary, so this is only an estimate.
How to use the Ovulation Calculator
- Enter first day of your last period.
- Enter average cycle length.
- Tap Calculate to see the result.
- Tap Reset to clear the fields and try again.
Who should use it
- People trying to conceive
- Anyone tracking their cycle
- Couples planning a pregnancy
Key terms
- Ovulation
- When an egg is released from the ovary.
- Fertile window
- The days when pregnancy is most likely.
- Cycle length
- Days from one period start to the next.
Frequently asked questions
How accurate is this?
It is an estimate based on an average cycle. Ovulation tests or tracking can be more precise.
Can I use this as birth control?
No. It is not reliable for preventing pregnancy.
What if my cycle is irregular?
Results will be less reliable. Ask your doctor.
Is this medical advice?
No. Consult a doctor.
Is my data stored?
No. Everything you enter stays in your browser and is cleared when you close the page.
Last updated: 1 November 2026